This invention relates to ignition resistant thermoplastic compositions made with thermoplastics such as styrene-butadiene-acrylonitrile copolymers, polyesters, polycarbonates, etc. and blends thereof containing polytetrafluoroethylene, metal salts of inorganic acids and organo phosphorous compounds which act to reduce the susceptibility of such compositions to ignition and/or burning or at least to minimize the dripping of molten polymer when exposed to fire conditions.
Thermoplastic polymers have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers are suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance, and excellent electrical properties are required.
However, these polymers exhibit a brief but definite burning time when contacted with an open flame.
In attempts to increase the combustion resistance of thermoplastic polymers, it has been a common practice to incorporate monomeric phosphites, phosphoric acid esters, thiophosphoric acid esters containing halogenated alkyl radicals and halogenated organic compounds into the carbonate polymer. However, in order to obtain any noticeable improvement in combustion resistance, these additives and/or combinations of the additives have been employed in such large quantities that they often adversely affect some of the desirable physical properties of the carbonate polymer such as heat stability, toughness, and ultra-violet light stability.
In U.S. Pat. No. 3,671,487 fire retardant polyester resins comprising glass fibers, fire retardant additives such as halogen-containing compounds or phosphate compounds and fibril forming polytetrafluoroethylene (PTFE) are disclosed and claimed. The present invention represents an improvement over this patent in that the need for glass fibers and halogenated compounds has been obviated.
U.S. Pat. No. 4,653,496 discloses the use of a combination of halogenated compound and metal oxides for ignition resistance of the blend of polycarbonate and acrylonitrile-butadiene-styrene copolymer (ABS). However, the metal oxides result in the thermal stability of PC.
U.S. Pat. No. 4,692,488 discloses a blend of a polycarbonate, a copolymer of styrene and acrylonitrile, triphenylphosphate, and tetrafluoropolyethylene. Comparison example 2 (line 53, page 8) of this patent indicates that without Na.sub.2 SO.sub.4, the blend of PC and ABS with triphenylphosphate and polytetrafluoroethylene give only V-1 rating.
British patent 1,459,648 discloses the use of triphenylphosphate, a non-combustible fibre material and polytetrafluoroethylene as flame retardant additives for PC, polyesters, and ABS. However, the patent shows that polytetrafluoroethylene resin does not prevent dripping without the addition of fibre.
Aromatic carbonate polymers having good flame retardant properties are shown in U.S. Pat. No. 4,626,563. However, the present invention represents an improvement over this patent also in that the need for halogenated compounds has been eliminated. The elimination of halogenated compounds is important since the presence of these compounds adversely effects the ultra-violet light stability of the polymers.